linux-kernel - Re: [PATCH nf v2] netfilter: conntrack: connection timeout after re-register

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Message-ID: <20201014082341.GA16895@breakpoint.cc>
Date:   Wed, 14 Oct 2020 10:23:41 +0200
From:   Florian Westphal <fw@...len.de>
To:     Pablo Neira Ayuso <pablo@...filter.org>
Cc:     Florian Westphal <fw@...len.de>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Francesco Ruggeri <fruggeri@...sta.com>,
        open list <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>, coreteam@...filter.org,
        netfilter-devel@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>,
        David Miller <davem@...emloft.net>
Subject: Re: [PATCH nf v2] netfilter: conntrack: connection timeout after
 re-register

Pablo Neira Ayuso <pablo@...filter.org> wrote:
> > Yes, we iterate table on re-register and modify the existing entries.
> 
> For iptables-nft, it might be possible to avoid this deregister +
> register ct hooks in the same transaction: Maybe add something like
> nf_ct_netns_get_all() to bump refcounters by one _iff_ they are > 0
> before starting the transaction processing, then call
> nf_ct_netns_put_all() which decrements refcounters and unregister
> hooks if they reach 0.

No need, its already fine.  Decrement happens from destroy path,
so new rules are already in place.

> The only problem with this approach is that this pulls in the
> conntrack module, to solve that, struct nf_ct_hook in
> net/netfilter/core.c could be used to store the reference to
> ->netns_get_all and ->net_put_all.
> 
> Legacy would still be flawed though.

Its fine too, new rule blob gets handled (and match/target checkentry
called) before old one is dismantled.

We only have a 0 refcount + hook unregister when rules get
flushed/removed explicitly.